Sensitivity and specificity analysis for targeted selective treatment using eye colour chart in sheep flocks naturally infected with Haemonchus contortus

C P SWARNKAR; D SINGH

doi:10.56093/ijans.v84i11.44719

Authors

C P SWARNKAR Central Sheep and Wool Research Institute, Avikanagar, Rajasthan 304 501 India
D SINGH Central Sheep and Wool Research Institute, Avikanagar, Rajasthan 304 501 India

https://doi.org/10.56093/ijans.v84i11.44719

Keywords:

Anaemia, Eye colour chart, Haemonchus contortus, Sensitivity, Sheep, Specificity, Targeted selective treatment

Abstract

An eye color chart for screening the flock for anaemic sheep was developed and is in use since 2008 in organized farms in arid Rajasthan. In present analysis its accuracy (sensitivity and specificity) was analyzed in identifying anaemic sheep (PCV <18 or <22) and to quantify the proportion of sheep left untreated when using it for management of Haemonchus contortus. A linear trend was observed in proportion of true positives and level of FECs in all the seasons at both the PCV cut-off values. The percentage of correct treatment was maximum (71.3 to 83.4%) with moderate kappa index in individuals with intensity of infection >3001 epg. An inverse relation exists between sensitivity and specificity of the TST system. Based on criteria, the overall sensitivity of TST system ranged from 22.9% (criteria as FEC <1000 epg and PCV <18) to 90.1% (criteria as FEC >3001 epg and PCV <22). In visually anaemic animals, the sensitivity was lower when PCV cut-off <18% was considered positive test results. In highly infected animals, the sensitivity of TST system remained >85% during both monsoon season and winter. The overall specificity varied from 20.0 (criteria as FEC >3001 epg and PCV <22) to 81.5% (criteria as FEC <1,000 epg and PCV <18). Thus it appears that in sheep flocks predominantly infected with H. contortus, the application of the TST system as a guidance for the administration of anthelmintic drugs can be an important tool in management of GINs in Rajasthan.

Downloads

Download data is not yet available.

References

Altman D G, Machin D, Bryant T N and Gardner M J. 2000. Statistics with Confidence. 2nd edn, p. 240. BMJ Books, London.

Cringoli G, Veneziano V, Jackson F, Vercruysse J, Greer A W, Fedele V, Mezzino L and Rinaldi L. 2008. Effects of strategic anthelmintic treatments on the milk production of dairy sheep naturally infected by gastrointestinal strongyles. Veterinary Parasitology 156: 340–45. DOI: https://doi.org/10.1016/j.vetpar.2008.06.015

Ejlertsen M, Githigia S M, Otieno R O and Thamsborg S M. 2006. Accuracy of an anaemia scoring chart applied on goats in sub humid Kenya and its potential for control of Haemonchus contortus infections. Veterinary Parasitology 141: 291–301. DOI: https://doi.org/10.1016/j.vetpar.2006.05.020

Kaplan R M, Burke J M, Terrill T H, Miller J E, Getz W R, Mobini S, Valencia E, Williams M J, Williamson L H, Larsen M and Vatta A F. 2004. Validation of the FAMACHA eye color chart for detecting clinical anaemia in sheep and goats on farms in the southern United States. Veterinary Parasitology 123: 105–20. DOI: https://doi.org/10.1016/j.vetpar.2004.06.005

Knox M R, Torres-Acosta J F J and Aguilar-Caballero A J. 2006. Exploiting the effect of dietary supplementation of small ruminants on resilience and resistance against gastrointestinal nematodes. Veterinary Parasitology 139: 385–93. DOI: https://doi.org/10.1016/j.vetpar.2006.04.026

Le Jambre L F. 1995. Relationship of blood loss to worm numbers, biomass and egg production in Haemonchus contortus infected sheep. International Journal for Parasitology 25: 269–73. DOI: https://doi.org/10.1016/0020-7519(94)00118-8

MAFF. 1986. Manual of Veterinary Parasitological Techniques. Vol. 18. Ministry of Agriculture, Fisheries and Food, London. Malan F S, Van Wyk J A and Wessels C D. 2001. Clinical evaluation of anaemia in sheep: early trials. Onderstepoort Journal of Veterinary Research 68: 165–74.

Reynecke D P, van Wyk J A, Gummow B, Dorny P and Boomker J. 2011. Validation of the FAMACHA© eye colour chart using sensitivity / specificity analysis on two South African sheep farms. Veterinary Parasitology 177: 203–11. DOI: https://doi.org/10.1016/j.vetpar.2009.08.023

Schalm O W, Jain N C and Carroll E J. 1975. Veterinary Haematology. 3rd edn, pp 15–81. Lea and Febiger, Philladelphia, USA.

Singh D and Swarnkar C P. 2010. Harnessing the advantages of over-dispersion in faecal egg counts through targeted selective treatment and breeding for diseases resistance. In: XX National Congress of Indian Association for the Advancement of Veterinary Parasitology, CCS HAU, Hisar, Haryana, 18 - 20 February.

Singh D and Swarnkar C P. 2012. Evaluation of targeted selective treatment strategy in sheep farm of Rajasthan. Indian Journal of Animal Sciences 82: 679–86.

Sotomaior C S, Rosalinski-Moraes F, de Costa A R B, Maria D, Monteiro A L G and van Wyk J A. 2012. Sensitivity and specificity of the FAMACHA© system in Suffolk sheep and cross Boer goats. Veterinary Parasitology 190: 114–19. DOI: https://doi.org/10.1016/j.vetpar.2012.06.006

Soulsby L. 2007. New concepts in strongyle control and anthelmintic resistance: the role of refugia. Veterinary Journal 174: 6–7. DOI: https://doi.org/10.1016/j.tvjl.2006.08.005

Swarnkar C P and Singh D. 2010. Questionnaire Survey on sheep husbandry and worm management practices adopted by farmers in Rajasthan. Indian Journal of Small Ruminants 16: 199–209.

Swarnkar C P and Singh D. 2012. Seasonal variation in efficacy of anthelmintics and prevalence of anthelmintic resistance in gastrointestinal nematodes of sheep in Rajasthan Indian Journal of Animal Sciences 82: 451–56.

Swarnkar C P, Singh D and Kumar S. 2012. Prevalence of benzimidazole resistant β-tubulin alleles in Haemonchus contortus larvae from sheep of Rajasthan. Indian Journal of Animal Sciences 82: 1477–81.

Thrusfield M V. 2005. Veterinary Epidemiology. 3rd edn., Blackwell, Cambridge.

Van Wyk J A and Bath G F. 2002. The FAMACHA© system for managing haemonchosis in sheep and goats by clinically identifying individual animals for treatment. Veterinary Research 33: 509–29. DOI: https://doi.org/10.1051/vetres:2002036

van Wyk J A, Hoste H, Kaplan R M and Besier R B. 2006. Targeted selective treatment for worm management - how do we sell rational programs to farmers? Veterinary Parasitology 139: 336–46. DOI: https://doi.org/10.1016/j.vetpar.2006.04.023

Vatta A F, Letty B A, van der Linde M J, van Wijk E F, Hansen J W and Krecek R C. 2001. Testing for clinical anaemia caused by Haemonchus spp. in goats farmed under resource-poor conditions in South Africa using an eye colour chart developed for sheep. Veterinary Parasitology 99: 1–14. DOI: https://doi.org/10.1016/S0304-4017(01)00446-0

Vercruysse J, Jackson F, Besier B and Pomroy B. 2009. Novel solutions for the sustainable control of nematodes in ruminants (PARASOL). Veterinary Parasitology 164: 1–2. DOI: https://doi.org/10.1016/j.vetpar.2009.04.025